Chemical inorganic fertilizers such as ammonium phosphates, ammonium nitrates, potassium nitrates, potassium chlorides, potassium sulfates and many others are well known fertilizers. Methods of manufacturing these inorganic fertilizers as well as methods of processing the fertilizers into particles are also well known in the fertilizer art. The resulting fertilizer particles, however, exhibit at least one undesirable characteristic. The caking of various types of fertilizers interferes with the handling of fertilizers in bulk form at the factory and by the end user.
Caking is believed to be caused by several factors, e.g., the formation of crystalline bridges according to which solid connections are formed at the points of contact among the granules. Alternatively, there may be capillary adhesion or bonding between the granules with a significant force often being necessary to break this adhesion or bonding. The cohesive forces will vary depending upon the storage conditions and other variables. The hygroscopic nature of the fertilizers also results in undesirable caking. In all cases however, the caking causes a serious problem to which a completely satisfactory solution is lacking.
Several prior art methods have been proposed to decrease fertilizer caking which involve the use of additives to the fertilizer composition. Typical additives include the use of finely divided powders which must cover the fertilizer substantially uniformly such as for example talc, kaolin and diatomaceous earth. Surfactants may also be used, e.g., non-ionic surfactants, such as polyoxylenes and anionic surfactants, e.g., alkyl-aryl-sulfonates and in particular the sulfonates derived from benzene and naphthalene. Cationic surfactants have also been used, especially the amines derived from long chain fatty acids. These additives form a hydrophobic film around the fertilizer granules and simultaneously reduce the surface tension of the intergranular solution, lower the angle of contact and thereby exert a beneficial effect on the caking problem. Further additives include compounds that also tend to form a hydrophobic film around the fertilizer granules such as paraffin wax, polyolefin wax and mineral oils. However, it has been found that the compositions used heretofore are not entirely effective in eliminating the caking problem. Moreover, many of these additives are not desirable in the fertilizer composition, others are expensive and require relatively large amounts thereof.
Various types of anti-caking additives include those disclosed in the following references.
U.S. Pat. Nos. 5,041,153, 5,032,164 and 4,846,871 disclose the use of lignosulfonate to treat inorganic chemical fertilizers to harden the particles to provide anti-caking and anti-dusting properties by adding up to about 5.0% by weight of lignosulfonate to the fertilizer.
U.S. Pat. No. 4,772,308 discloses an anti-caking composition for nitrogen-containing material consisting essentially of ammonium salts useful as an ingredient of fertilizer, e.g., sodium alkyl sulfates, potassium alkyl sulfates or monoethanolammonium alkyl sulfate, diethanolammonium alkyl sulfate and triethanolammonium alkyl sulfate.
Heretofore, the use of tripotassium phosphate as an anti-caking agent for fertilizers has not been achieved, although tripotassium phosphate has been used for other purposes, as set forth in the following exemplary references.
U.S. Pat. No. 3,791,809 discloses a method of strengthening glass articles using powdered salts as the ion exchange medium, e.g., tripotassium phosphate, and utilizes cornstarch and flocculent silica as anti-caking agents.
U.S. Pat. No. 3,609,089 discloses the use of tripotassium phosphate as an alkaline builder in a process and composition for cleaning road vehicles, while silicate, silica gel and similar materials provide a non-caking function.
U.S. Pat. No. 4,066,390 discloses the use of tripotassium phosphate as a pH buffer.
Therefore, a need exists for an anti-caking agent to be used in inorganic fertilizers.